1. Field of the Invention
The present invention relates to a dispersion of a conductive polymer, in particular a polymer or copolymer of a substituted or unsubstituted thiophene, and a polyanion in a non-aqueous dispersion medium. The present invention also relates to a method of preparing such a dispersion from a freeze dried composition comprising a conductive polymer, in particular a polymer or copolymer of a substituted or unsubstituted thiophene, and a polyanion.
2. Description of the Related Art
The preparation of polythiophenes and dispersions thereof for use in antistatic coatings has been described in the literature e.g. ‘Handbook of Organic Conductive Molecules and Polymers’, ed. H. S. Nalwa, J. Wiley & Sons, 1997. Polythiophenes have conductive properties.
In large scale methods for preparing aqueous dispersions of a latex comprising a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene, the solid content of the aqueous dispersions is limited to only a few percent, due to production reasons such as the need for ultrafiltration, the viscosity of the dispersion etc. It should be noted that such dispersions are often erroneously referred to as solutions due to the very small particle size, i.e. 20 to 50 nm, of the polythiophene/polyanion latex. Shipment of such dilute dispersions is expensive and cumbersome in view of the high volume and weight associated therewith.
For instance, PEDOT, i.e. poly(3,4-ethylenedioxythiophene) in combination with PSS (PSS as used in the present disclosure stands for poly(styrene sulfonic acid) or poly(styrene sulfonate)), is produced industrially as an aqueous dispersion of approximately 1 wt % of PEDOT/PSS. However many potential applications for PEDOT/PSS require a non-aqueous dispersion in which the concentration of water is as low as possible, while retaining or increasing the concentration of thiophene polymers or co-polymers. Various methods such as e.g. simple evaporation of the water (WO99/34371), dehydratation by dialysis (WO02/42352), azeotropic distillation (WO 02/072660), flash evaporation (WO 03/087222) and solvent addition followed by evaporation of the water (WO 03/48228, WO 03/048229) have been investigated to obtain these concentrated dispersions.
EP-A 1801143 discloses a coating solution or dispersion comprising a redispersible or soluble product obtainable as a dry product or as a paste by freeze drying an aqueous dispersion of a latex comprising a polyanion and a polymer or copolymer of a substituted or unsubstituted thiophene. The water content of the coating solution or dispersion may be less than 12 wt %, preferably less than 6 wt % relative to the total weight of the dispersion.
The presence of water in a non-aqueous dispersion of a polymer or copolymer of a substituted or unsubstituted thiophene and a polyanion may have a negative influence on the conductivity of coatings obtained from such dispersions. Also, in some applications wherein conductive polymers may be used, for example OLED, OPV (Organic Photovoltaic), Dye Sensitized Solar Cells (DSSC) and also solar cells based on Perovskites, the presence of a minor amount of water may have a detrimental effect on the performance and lifetime of the devices.